Love Lawson's Glowire. I use it on all my tarps and have replaced the guylines on my tents with this. Super strong, lightweight and bright when your headlamp hits it. And, plenty of colors, so you can pick your favorite (though, the correct answer is obviously YELLOW).
TAGinAZNaw, the correct answer is Orange. So easy to see. I'm slowly replacing all the guylines on my tents with it after using it on my hammock tarps.